1. Field of the Invention
The present invention is directed to vapor flow and hydrocarbon concentration sensors that are positioned in a vapor recovery line for a fuel dispenser.
2. Description of the Prior Art
Vapor recovery equipped fuel dispensers, particularly gasoline dispensers, have been known for quite some time, and have been mandatory in California for a number of years. The primary purpose of using vapor recovery is to retrieve or recover the vapors, which would otherwise be emitted to the atmosphere during a fueling operation, particularly for motor vehicles. The vapors of concern are generally those which are contained in the vehicle gas tank. As liquid gasoline is pumped into the tank, the vapor is displaced and forced out through the filler pipe. Other volatile hydrocarbon liquids raise similar issues. In addition to the need to recover vapors, some states, California in particular, are requiring extensive reports about the efficiency with which vapor is recovered.
A traditional vapor recovery system is known as the xe2x80x9cbalancexe2x80x9d system, in which a sheath or boot encircles the liquid fueling spout and connects by tubing back to the fuel reservoir. As the liquid enters the tank, the vapor is forced into the sheath and back toward the fuel reservoir or underground storage tank (UST) where the vapors can be stored or recondensed. Balance systems have numerous drawbacks, including cumbersomeness, difficulty of use, ineffectiveness when seals are poorly made, and slow fueling rates.
As a dramatic step to improve on the balance systems, Gilbarco, Inc., assignee of the present invention, patented an improved vapor recovery system for fuel dispensers, as seen in U.S. Pat. No. 5,040,577, now Reissue Pat. No. 35,238 to Pope, which is herein incorporated by reference. The Pope patent discloses a vapor recovery apparatus in which a vapor pump is introduced in the vapor return line and is driven by a variable speed motor. The liquid flow line includes a pulser, conventionally used for generating pulses indicative of the liquid fuel being pumped. This permits computation of the total sale and the display of the volume of liquid dispensed and the cost in a conventional display, such as, for example as shown in U.S. Pat. No. 4,122,524 to McCrory et al. A microprocessor translates the pulses indicative of the liquid flow rate into a desired vapor pump operating rate. The effect is to permit the vapor to be pumped at a rate correlated with the liquid flow rate so that, as liquid is pumped faster, vapor is also pumped faster.
There are three basic embodiments used to control vapor flow during fueling operations. The first embodiment is the use of a constant speed vapor pump during fueling without any sort of control mechanism. The second is the use of a pump driven by a constant speed motor coupled with a controllable valve to extract vapor from the vehicle gas tank. While the speed of the pump is constant, the valve may be adjusted to increase or decrease the flow of vapor. The third is the use of a variable speed motor and pump as described in the Pope patent, which is used without a controllable valve assembly. All three techniques have advantages either in terms of cost or effectiveness, and depending on the reasons driving the installation, any of the three may be appropriate, however none of the three systems, or the balance system are able to provide all the diagnostic information being required in some states. The present state of the art is well shown in commonly owned U.S. Pat. No. 5,345,979, which is herein incorporated by reference.
Regardless of whether the pump is driven by a constant speed motor or a variable speed motor, there is no feedback mechanism to guarantee that the amount of vapor being returned to the UST is correct. A feedback mechanism is helpful to control the A/L ratio. The A/L ratio is the amount of vapor-Air being returned to the UST divided by the amount of Liquid being dispensed. An A/L ratio of 1 would mean that there was a perfect exchange. Often, systems have an A/L greater than 1 to ensure that excess air is recovered rather than allowing some vapor to escape. This inflated A/L ratio causes excess air to be pumped into the UST, which results in a pressure build up therein. This pressure build up can be hazardous, and as a result most USTs have a vent that releases vapor-air mixtures resident in the UST to the atmosphere should the pressure within the UST exceed a predetermined threshold. While effective to relieve the pressure, it does allow hydrocarbons or other volatile vapors to escape into the atmosphere.
While PCT application Ser. No. PCT/GB98/00172 published Jul. 23, 1998 as WO 98/31628, discloses one method to create a feedback loop using a Fleisch tube, there remains a need to create alternate feedback mechanisms to measure the vapor flow in a vapor recovery system. Specifically, the feedback needs to not only tell the fuel dispenser how fast vapor is being recovered, but also how efficiently the vapor is being recovered. To do this, the feedback mechanism needs to monitor vapor flow and hydrocarbon concentration in the vapor return path. Not only should the feedback mechanism improve the efficiency of the vapor recovery operation, but also the feedback mechanism should be able to report the information being required by California""s increased reporting requirements.
The deficiencies of the prior art are addressed by providing a vapor flow sensor and a hydrocarbon concentration sensor in a vapor return line for a fuel dispenser. As used herein a xe2x80x9chydrocarbon sensorxe2x80x9d includes sensors that directly measure the concentration of hydrocarbons as well as sensors that indirectly measure the concentration of hydrocarbons, such as by measuring oxygen concentration. The combination of sensors allows more accurate detection of hydrocarbons being recovered by the vapor recovery system. This is particularly helpful in determining if an Onboard Recovery Vapor Recovery (ORVR) system is present in the vehicle being fueled. When an ORVR system is detected, the vapor recovery system in the fuel dispenser may be turned off or slowed to retrieve fewer vapors so as to avoid competition with the ORVR system. Additionally, the combined sensor allows a number of diagnostic tests to be performed which heretofore were not possible.
The combination of sensors may be positioned in a number of different locations in the vapor recovery line, or even in the vent path for the Underground Storage Tank (UST). The exact position may determine which diagnostic tests may be performed, however, the sensors should allow a number of diagnostic tests regardless of position. In this manner data may be collected to comply with the California Air Resources Board (CARB) regulations.